This has now been added to pshvm.codeplex.com a free powershell hyper-v manager project.
Connect/Access your VM while OS being installed or if you need to add and IP address
read all about it and download it from there but here is a work around if you find yourself faced with needing to send a crtl+alt+del to a VM via the freeRDp interface.
So far there is no crtl+alt+del button so you have two work arounds. The first one assumes you are RDP'ed into the VHOST so you can press crt+alt+end, then you can press esc to get out this screen:
Now minimize, then maximize your VHOST RDP session so you can now type in the password field. Yeah I found that one by accident.
Or once you get the RDP screen to open you can use this button
then choose these options, click Apply and OK.
Now you will see this on screen keyboard, click the Ctrl, click the Alt, click and hold the Del
if you did it right you will see you can now type the Administrator PWD.
I find it easiest to use the ease of access button again, uncheck the three boxes, apply and save and then close the onscreen keyboard and type the Administator password with my normal keyboard.